Joke's on her, he has called her darling twice in this conversation. Yeager notes never to use a possessive with darling, that would definitely move Rita's temper from angry to explosive. His grin widens for a bit, before he looks extra hurt.

"Leibchen, if I knew the answers, I would apply them to save myself from any further tailor fees!" And now it's three times. "And don't you think that I would have used this trick in my poor watery grave, if it was something of my doing? Tsk, tsk, I had thought you quite the intelligent girl~"